Google announced last fall that the old Office formats would no longer be supported as of 2013 and that users would need to make adjustments.

Google Docs users have known since last fall that they'd soon no longer be able to export files to older Microsoft Office formats. Now the drop-dead deadline of Jan. 31 is fast approaching, and Google Docs wants to remind users of the coming changes.
The changes were announced Sept. 25, 2012, with an original planned transition date of Oct. 1, 2012, but users protested to Google that a week's notice wouldn't give them enough time to make the needed changes. The company was ultimately forced to push the transition to Jan. 31 to give Docs users more time to get ready.
As of the end of this month, the transition will now be made, according to a Jan. 17 post on the Google Apps blog.
"In September, we added the ability to export Google documents to the newer Microsoft Office formats that rely on open standards (.docx, .xlsx, .pptx)," the post reported. "To continue adding new features and innovations to Google Drive and Docs, we'll be focusing our resources on exporting to these newer open formats rather than the older, proprietary Office formats (.doc, .xls, .ppt) that were used in Office 97-2003."

The changes will mean that after Jan. 31, "users will not be able to export files to the older Office 97-2003 formats," the post reported. "For users who still use Office 97-2003, we recommend installing the free compatibility plug-in from Microsoft, which will allow them to open the modern Office file types."

The Google Docs built-in exporting feature allows users to directly export Docs files into Microsoft Office using formats recognized by Office. Google Docs had planned, however, to stop allowing file exports using the older formats supported by Microsoft Office versions from 1997 through 2003. Google was trying to transition Google Docs users only to do file exports directly to newer versions of Microsoft Office.

The proposed changes will relate to the use of the Google Docs file exports only, however, meaning that users would still be able to import Microsoft Office files of any format into Google Docs on their own, according to a Sept. 26 post on the Google Apps blog. Google is touting the move as a way to make it easier for Docs users to be able to export their Google Docs files into the latest Microsoft Office formats automatically for easier transfers with users of later editions of the Microsoft Office suite.
The built-in file export changes mean that files ending in older 1997 to 2003 Office formats, including .doc, .xls and .ppt, would have to be converted into the latest Microsoft Office formats, including .docx, .xlsx and .pptx, before they can be exported from Google Docs to Microsoft Office users.
While Google Docs is dropping support for the export of older Office formats, it will still maintain support for other existing file formats, including OpenDocument formats, plain text, JPG images and PDFs, according to Google.
The changes, even with their Jan. 31 delay, will still likely make it more complicated for Google Docs users to share files with users of older 1997 to 2003 versions of Office. That problem, of course, has arisen for Office users every time Microsoft has changed its file formats, all in the name of progress, over the years. New Office formats always stress usability improvements, but make it more complicated to transfer files when different users run different versions of Office.
The latest Office formats, .docx, .xlsx and .pptx, are based on HTML, which wasn't supported under the 1997 to 2003 file formats.